Recovery of solvent in arylene sulfide polymer production

ABSTRACT

A polar organic solvent selected from amides, lactams, and sulfones is extracted from an aqueous solution containing alkali metal halide. In the production of arylene sulfide polymers by the reaction of a polyhalo-substituted aromatic compound with an alkali metal sulfide in a polar organic solvent, solids are removed from an aqueous mixture of the reaction effluent and polar organic solvent is recovered from the aqueous solution by extraction with a solvent. In a preferred embodiment N-methyl-2pyrrolidone is recovered from the aqueous solution by extraction with a solvent such as dichloromethane, chloroform, and 1,1,2,2tetrachloroethane.

United States Patent Crouch et al. 45 A 29, 1972 [54] RECOVERY OFSOLVENT IN 3,346,567 10/ 1967 Westerveld et al. ....260/239.3 ARYLENESULFIDE POLYMER 3,583,982 6/1971 Capp et al. ..260/239.3 PRODUCTION3,446,797 5/1969 Focella et al. ..260/239.3

[72] Inventors: Willie W. Crouch; Charles W. Prima ry Examiner-Donald E.CZa a Moberly, both of Bartlesvllle, Okla. Assistant L Marquis [73]Assignee: Phillips Petroleum Company Att0rneyY0ung and Q gg [22] Filed:NOV- 9, [21] Appl' 88,199 A polar organic solvent selected from amides,lactams, and sulfones is extracted from an aqueous solution 52 us. c1..260/79.1, 260/79, 260/2393 A, containing alkali metal halide theProduction of 260/3265 FN 260/551 P 260/561 R arylene sulfide polymersby the reaction of a polyhalo- 260/6O7 substituted aromatic compoundwith an alkali metal 51 Int. Cl. ..C08g 23/00 Sulfide in a P0lalr garlicSwen" S1ids are rammed [58] Field of search 260/79 791 326.5 FN 607 Afrom an aqueous mixture of the reaction effluent and 6 6 A 561 a 551polar organic solvent is recovered from the aqueous solution byextraction with a solvent. In a preferred [56] References Citedembodiment N-methyl-Z-pyrrolidone is recovered from the aqueous solutionby extraction with a solvent UNITED STATES PATENTS such asdichloromethane, chloroform, and l,1,2,2-

t hl h 3,354,129 11/1967 Edmonds, Jr. et al ..260/79 t6 met me 3,532,67710/ 1970 Baron ..260/79.3 5 Claims, No Drawings RECOVERY OF SOLVENT INARYLENE SULFIDE POLYMER PRODUCTION BACKGROUND OF THE INVENTION Thisinvention relates to processes for the production of polymers fromaromatic compounds. In one of its aspects, this invention relates toprocesses for the production of arylene sulfide polymers. In another ofits aspects, this invention relates to the separationinto solid andliquid components of the reaction mixture of the reaction ofpolyhalo-substituted aromatic compounds with alkali metal sulfidein apolar organic solvent. In still another of its aspects, this inventionrelates to the extraction of polar compounds from aqueous solutions. Inyet another of its aspects, this invention relates to the recovery ofpolar solvents from the reaction mixture of the reaction ofpolyhalo-substituted aromatic compounds with an alkali metal sulfide ina polar organic solvent.

In one concept of the invention it provides a method for separating thesolid and liquid components of the reaction of polyhalo-substitutedaromatic compounds with an alkali metal sulfide in a polar organicsolvent by filtration, centrifugation, or other mechanical means. Inanother of its concepts this invention provides a method for recoveringa polar organic solvent from an aqueous solution by extraction withspecified compounds. In still another of its concepts, this inventionprovides a method for recovery of a polar organic solvent from thereaction mixture of the reaction of a polyhalo-substituted aromaticcompound with an alkali metal sulfide in a polar organic solvent byseparation of the solid and liquid portions of the reaction mixturefollowed by extraction of the polar solvent from the liquid.

A process for the production of arylene sulfide polymers frompolyhalo-substituted cyclic compounds containing unsaturation betweenadjacent ring atoms, wherein the halogen atoms are attached to ringcarbon atoms with an alkali metal sulfide in a polar organic compound atan elevated temperature is disclosed in U.S. Pat. No. 3,354,129. To makesuch a process commercially desirable suitable means must be found forrecovery of the organic solvent used in the process. Various knownprocesses and combinations of processes for recovery of a polar organicsolvent from a reaction mixture can be proposed. However, the order inwhich a combination of steps is performed is important in yieldingcommercially acceptable results. Having determined the use of acombination of processes the success of which depends on definitephysical or chemical characteristics of the compounds acted upon, suchas the process of extraction, the choice of agents for carrying out theprocess, i.e., extractants, is paramount to the success of the process.

Accordingly, it is an object of this invention to provide a method forrecovering the polar organic solvent from the reaction mixture of thereaction of polyhalosubstituted aromatic compounds with an alkali metalsulfide in a polar organic solvent.

It is another object of this invention to provide a method forseparating the solid and liquid materials of the reaction mixture ofpolyhalo-substituted aromatic compounds with an alkali metal sulfide ina polar organic solvent.

It is still another object of this invention to provide a method forrecovering polar organic solvent from the aqueous solution produced inremoving solids from the reaction mixture in the reaction ofpolyhalo-substituted aromatic compounds with an alkali metal sulfide ina polar organic solvent.

Other aspects, objects and advantages of this invention will be apparentto one skilled in the art upon reading the specification and theappended claims.

SUMMARY OF THE INVENTION In accordance with this invention, a polarorganic solvent chosen from among amides, lactams and sulfones isrecovered from an aqueous solution containing alkali metal halide byextraction with an extractant selected from among dichloromethane,chloroform, 1,2-dichloroethane, l ,1 ,2-trichloroethane, l, l ,2,2-tetrachloroethane, trichloroethylene, l-hexanol, cyclohexanol, methylisobutyl ketone, aniline, and mixtures thereof.

In accordance with an embodiment of this invention, in the production ofarylene sulfide polymers by the reaction of polyhalo-substitutedaromatic compounds with an alkali metal sulfide in a polar organicsolvent, solid materials are removed from an aqueous mixture of thereaction effluent; polar organic solvent is recovered from the aqueousmixture by extraction with a selected extractant and the polar organicsolvent is separated from the extractant.

The process of this invention is particularly useful in the recovery ofpolar organic solvent employed in the production of arylene sulfidepolymers by the process of U.S. Pat. No. 3,354,129. Thus, the process ofthe instant invention is useful in the recovery of polar organicsolvents which are solvents for the polyhalo aromatic compounds and thealkali metal sulfides used in the production of the arylene sulfidepolymers. Examples of such polar organic solvents include amides,including lactams, and sulfones. Specific examples of such polar organicsolvents include hexamethylphosphoramide, tetramethylurea,N,N-ethylenedipyrrolidone, N- methyl-Z-pyrrolidone (NMP), pyrrolidone,caprolactam, N-ethylcaprolactan, sulfolane, N,N- dimethylacetamide, lowmolecular weight polyamides, and the like. The polar organic solventpresently preferred is N-methyI-Z-pyrrolidone (NMP).

In a preferred embodiment, the polymerization reaction effluentcomprising arylene sulfide polymer, alkali metal halide, polar organicsolvent, and minor amounts of impurities is mixed with an amount ofwater sufficient to provide 0.01 to 100, preferably 1 to 20, parts byweight water per part by weight polar organic solvent. The arylenesulfide polymer is then separated by filtration, centrifugation or othermechanical means from the aqueous solution, containing polar organicsolvent and alkali metal halide. A portion of the water, instead ofbeing added directly to the polymerization reaction effluent as above,can be used first to wash arylene sulfide polymer previously separatedfrom the bulk of the solution. Alternatively, the washings can be addedto the aqueous solution containing polar organic solvent and alkalimetal halide subsequent to removal of arylene sulfide polymer.

The aqueous solution is then extracted. The extractant suitable for usein this invention is selected from 3 the group consisting ofdichloromethane, chloroform, 1 ,2-dichloroethane, 1,1,2-trichloroethane, 1,1,2,2- tetrachloroethane, trichloroethylene,l-hexanol, cyclohexanol, methyl isobutyl ketone, aniline, and mixturesthereof. The preferred extractants are dichloromethane, chloroform, 1 ,1,2,2-

tetrachloroethane, cyclohexanol, and aniline. The extractants mostpreferred are dichloromethane, chloroform and 1,1,2,2-tetrachloroethane.

Suitability of the above extractants in the process of this invention isbased on a number of characteristics of the extractants. Theseextractants have (1) a low solubility in water an in aqueous alkalimetal halide solutions, (2) a large distribution coefficient for thepolar organic solvent to be extracted so that large quantities ofextractant are not required, (3) a relatively low cost, (4) a reasonableheat of vaporization to allow a saving in heat requirement overvaporization of the water present, (5) distillation characteristics topermit relatively easy separation from polar organic solvent, and (6) adensity sufficiently different from that of the aqueous solution topermit good phase separation.

The weight ratio of extractant to aqueous solution generally is withinthe range of about 1:1 to :1, preferably about 1:1 to 7:1. Although theextraction can be carried out over a broad temperature range, theextraction temperature generally will be within the range of about 0200C, preferably about 20100 C. Although elevated pressures, e.g.,pressures up to about 20 atmospheres or more, can be employed,substantially atmospheric pressure is preferred. In any event, thepressure should be sufficient to maintain the components of the systemsubstantially in the liquid phase. Although the extraction can becarried out batchwise, e.g., in a multiple extraction process,extraction in a continuous process is preferred.

Method for separating the polar organic solvent from the extractant canvary depending on the solvent and extractant used. The usual method ofseparation is distillation the techniques for which are so well knownthat discussion here is not necessary. As mentioned above one of thecriteria for choosing a suitable extractant for this process isdistillation characteristics to permit relatively easy separation of thepolar organic solvent from the extractant.

The following specific examples are offered to show the effectiveness ofthe extractants chosen for accomplishing the extraction of the polarorganic solvent from the aqueous mixture of the reaction effluent by theprocess of this invention. These examples are meant to be illustrativeand not exclusive.

EXAMPLE 1 A series of solutions of 25.0 g. of N-methyl-2-pyrrolidone(NMP) and 69.8 g. of 10.6 weight per cent sodium chloride in water wasprepared. This composition was designed to simulate the filtrateobtained upon filtering arylene sulfide polymer from a mixture of waterand reaction effluent from the reaction of a polyhalo-substitutedaromatic compound with sodium sulfide in NMP. Each of the solutions wasextracted at about 25 C with 25 g. of an extractant, and the weight percent NMP in the extractant phase was determined by gas chromatographicanalysis. The NMP content of the extractant phase obtained through useof each of the extractants is shown in Table I.

TABLE 1 Weight Percent NMP Exu'actam in Extractant Phase Dichloromethane25.5 Chloroform 23.6 Aniline 22.5 Cyclohexanol 22.41,1,2,2-Tetrachloroethane 20.9 l-Hexanol 15.7 1,1,2-Trichloroethane 14.61,2-Dichloroethane 13 .7 Trichloroethylene 5.7 Methyl isobutyl ketone2.4

Thus, each of the above extractants was effective in extracting NMP froman aqueous solution containing sodium chloride and NMP.

EXAMPLE II A series of mixtures containing varying ratios ofdichloromethane (DCM), N-methyl-Z-pyrrolidone (NMP), and either water orwater containing 5.7 weight per cent sodium chloride was prepared, andthe mixtures were shaken and then allowed to separate into phases atabout 25 C. The phases were separated, weighed, and analyzed by gaschromatography. Table 11 shows the composition of the series of mixturesas well as the weight and composition of the phases which wereseparated. Additionally, Table II shows the density of the DCM and waterphases from each of four of the extractions.

TABLE II.SYSTEM: DCM-NMP-WATER Composition of mixture DCM phase Waterphase composition weight, com osition wei ht Weight percent Weight, g.liCM @8581 percent p percent g p ase, p ase Extraction DCM NMP H20 DCMNMP H2O g. g. DCM NMP. H2O DCM NMP H20 SYSTEM: DCMNMP5.7 WEIGHT PERCENTSALT WATER In Extractions 5-8 values for weight of H10 and weightpercent 11 0 include NaCl present.

Density of phases from extractions 5-8, g./cm.

Thus, DCM effectively extracted NMP from aqueous solutions of NMP in thepresence or absence of sodium chloride. The difference in densitybetween the dichloromethane phase and the water phase, even when thewater phase contained sodium chloride, was sufficiently different topermit good separation of the phases.

EXAMPLE III A series of mixtures consisting of N-methyl-2-pyrrolidone(NMP) and water containing varying amounts EXAMPLE IV Table IV. In theTable the values shown for weight of water and weight per cent waterinclude any sodium chloride present.

TABLE IV.SYSTEM: CHLOROFORMNMP5.7 WEIGHT PERCENT SALT WATER Compositionof mixture Extract phase composition Water phase composition Weightpercent Weight, g. weight percent weight percent Extractant NMP H2OExtractant NMP H2O Extractant NMP H Extraetant NMP H20 45 20 35 90 40 707s. 9 20. 1 1. o 1. 5 2o. 5 7s. 0 37.5 40 22.5 75 so 45 51. 2 55. 5 a. 25. 9 43. 1 51. 0

svsrnm; 1,1,2,2-'IETRACIILOROE'IIIANE-NMP5.7 WEIGHT PERCENT SALT WATER45 20 35 no 40 70 79. 9 l8. s 1. s 0. 74 2a. 9 75. 4 37.5 4o 22. 5 75 so45 5o. 2 35.6 4. 2 5. 9 45. 2 4a. 9

of sodium chloride was extracted with Thus, chloroform andl,1,2,2-tetrachlorethane were dichloromethane (DCM) at about 25 C. Thephases were separated and analyzed by gas chromatography. The sodiumchloride concentration, when determined, was obtained by flame emissionspectroscopy. Additionally, a multiple extraction of a mixture of 10.6weight per cent aqueous sodium chloride and NMP was effective inextracting NMP from aqueous sodium chloride solutions of NMP.

pended claims of the invention the essence of which is made using ineach extraction a weight of DCM equal that there has been provided amethod for recovering a polar organic solvent from an aqueous solutionby extraction with specified chemical compounds.

We claim:

1. A method for recovering N-methyl-2-pyrrolidone from an aqueousreaction mixture solids slurry obtained by reacting apolyhalo-substituted aromatic compound and an alkali metal sulfide inN-methyl-2- pyrrolidone with subsequent slurrying by water dilu- TABLEIII Phase composition, weight percent NaCl NaCl Composition of mixture,g. DCM phase Water phase in DCM in water DCM, phase, phase, Water NaClNMP g. DCM NMP H2O DCM NMP H20 p.p.m ppm MULTIPLE EXTRACTION From 4thextraction 25. 0 91. 1 8. 5 0. 4 2. 0 6. 6

From 9th extraction 25. 0 98. 1. 15 0. 2 2. 0 0.40

Thus, DCM was effective in extracting NMP from solutions of NMP in watercontaining sodium chloride over a wide range of concentrations. Quiteimportant for the success of commercial operation was the finding thatthe amount of sodium chloride in the DCM phase was extremely small. Theresults of the multiple extraction gave further support for theapplicability of DCM as an extractant for recovering NMP from an aqueoussolution containing NMP.

tion, which method comprises:

a. separating the reaction mixture solids from the aqueous solution; b.extracting the N-methyl-2'pyrrolidone from said aqueous solution with anextractant selected from the group consisting of dichloromethane,chloroform, 1,2-dichloroethane, l ,l ,2- trichloroethane, l,l,2,2-tetrachloroethane,

trichloroethylene, l-hexanol, cyclohexanol,

methyl isobutyl ketone, aniline, and mixtures to 20:1 weight ratio ofextractant to aqueous solution within a temperature range of about 0 Cto about 200 C.

4. The method of claim 1 wherein the method of separating the solid andliquid components of the aqueous reaction mixture is chosen fromfiltration and centrifugation.

v5. The method of claim 1 wherein the extractant is selected from thegroup consisting of dichloromethane, chloroform, and l l,2,2-tetrachloroethanet

2. The method of claim 1 wherein the method of separating the polarorganic solvent and the extractant is by distillation.
 3. The method ofclaim 1 wherein extracting the N-methyl-2-pyrrolidone from an aqueoussolution which comprises an amount of water sufficient to provide 0.01to 100 parts by weight water per part by weight polar organic diluent isaccomplished at a ratio of 1:1 to 20:1 weight ratio of extractant toaqueous solution within a temperature range of about 0* C to about 200*C.
 4. The method of claim 1 wherein the method of separating the solidand liquid components of the aqueous reaction mixture is chosen fromfiltration and centrifugation.
 5. The method of claim 1 wherein theextractant is selected from the group consisting of dichloromethane,chloroform, and 1,1,2,2-tetrachloroethane.